Thank you for contacting Syncfusion support.
We have checked the reported scenario in UTC -5 and able to reproduce the issue in the version 15.1.0.41. In the presence of DST dates are not calculated correctly which is the cause for the issue, this know issue is fixed internally at our end. Fix for this issue will be included in our upcoming main release Volume 2, 2017 which is expected to be rolled out by the end of this month.
Regards,
Karthigeyan